JPH10235156A - Exhaust gas purifying catalyst bed, exhaust gas purifying catalyst coated structure and exhaust gas purifying method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas purifying catalyst bed capable of efficiently removing NOx in dilute combustion exhaust gas, a catalyst coated structure purifying exhaust gas and a method for purifying NOx in dilute combustion exhaust gas using them. SOLUTION: This catalyst A is obtained by adding silica and calcium, and if necessary, adding alumina and/or zirionia. This exhaust purifying catalyst constituted of the catalyst A and a catalyst B composed by adding silver to an alumina carrier having a pore structure wherein Y is 70% or more of X and Z is 20% or less of X when the total value of pore vol. occupying pores with a pore radius is 300Å or less is X and the total value of pore vol. occupying process with a pore radius of 25-100Å is Y and the total value of pore vol. occupying pores with a core radius of 100-300Å is Z in the relation of a pore radius and pore vol.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to exhaust gas used for purifying nitrogen oxides contained in combustion exhaust gas of mobile and stationary internal combustion engines of automobiles, boilers, gas engines, gas turbines, ships and the like. The present invention relates to a purification catalyst layer and an exhaust gas purification catalyst-coated structure, and more specifically, it can purify nitrogen oxides in exhaust gas discharged from an internal combustion engine operated in a lean burn region at a high space velocity and with high efficiency. The present invention relates to an exhaust gas purifying catalyst layer and an exhaust gas purifying catalyst coated structure, and an exhaust gas purifying method using the same.

[0002]

2. Description of the Related Art In a variety of combustion exhaust gas discharged from an internal combustion engine such as an automobile, nitrogen oxides (NOx) such as nitric oxide and nitrogen dioxide are included together with water and carbon dioxide as combustion products. include. NOx not only has an adverse effect on the human body, especially on the respiratory system, but also is one of the causes of acid rain, which is regarded as a problem from the viewpoint of global environmental protection. Therefore, development of a denitration technology for efficiently removing nitrogen oxides from these various exhaust gases is desired.

On the other hand, in view of the prevention of global warming, lean-burn internal combustion engines have recently attracted attention. A conventional gasoline engine for an automobile has an air-fuel ratio (A / F) = 1.
Combustion at a controlled stoichiometric ratio near 4.7. For exhaust gas treatment, carbon monoxide, hydrocarbons and NOx in the exhaust gas are converted to alumina mainly containing platinum, rhodium, palladium and ceria. A three-way catalyst system has been employed in which three harmful components are simultaneously removed by contact with a catalyst.

[0004] However, since the absolute condition is that the engine is operated at a stoichiometric ratio, the three-way catalyst system can be applied to exhaust gas purification of a lean burn gasoline engine operated at a lean air-fuel ratio. Can not. In addition, diesel engines are originally lean burn engines, but strict regulations are being imposed on both the suspended particulate matter and NOx in the exhaust gas.

Conventionally, as a method of reducing and removing the ΝOx in an oxygen-rich atmosphere, a technique of using NH ₃ also adsorb selectively catalyst small amount as the reducing gas has already been established. This technology has been industrialized as a method for denitration of exhaust gas from boilers and diesel engines, which are so-called fixed sources, but this method requires a special device for the recovery treatment of unreacted reducing agent, and also has an odor. Since it uses highly harmful ammonia, there is a danger that it cannot be applied particularly to a technique for denitration of exhaust gas from mobile sources such as automobiles.

In recent years, it has been reported that a NOx reduction reaction can be promoted by using unburned hydrocarbons remaining in a lean combustion exhaust gas in an oxygen-excess atmosphere as a reducing agent. Various catalysts have been developed and reported. For example, there are many reports that alumina or a catalyst in which a transition metal is supported on alumina is effective for a NOx reduction reaction using a hydrocarbon as a reducing agent. JP-A-4-284848 discloses that 0.1 to 4% by weight of Cu, Fe, Cr, Zn, Ni, V
Or silica-alumina containing ΝOx
An example of use as a reduction catalyst has been reported.

Further, when a catalyst in which Δt is supported on alumina is used, the NOx reduction reaction proceeds in a low temperature range of about 200 to 300 ° C., as disclosed in JP-A-4-267946 and JP-A-5-68855. Kaihei 5-1039
No. 49, for example. However, when these supported noble metal catalysts are used, the combustion reaction of hydrocarbons as a reducing agent is excessively promoted, and N ₂ O which is one of the substances causing global warming is by-produced, be advanced reduction reaction to harmless New ₂ selective had disadvantage is difficult.

One of the present applicants has previously found that the use of a catalyst containing silver with a hydrocarbon as a reducing agent in an oxygen-excess atmosphere causes the NOx reduction reaction to proceed selectively. -281844. Even after this disclosure was made, a similar ΝOx reduction and removal technique using a catalyst containing silver was disclosed in Japanese Patent Application Laid-Open No. 4-354536.
JP-A-5-92124, JP-A-5-92124
No. 125 and JP-A-6-277454.

[0009]

However, the alumina-supported silver catalysts described in these conventional publications are not suitable for SOx.
And the denitration performance in the presence of steam was still insufficient for practical use.

The present invention has been made to solve the above-mentioned drawbacks of the prior art, and an object of the present invention is to provide an exhaust gas purifying catalyst layer and an exhaust gas purifying method capable of efficiently removing NOx in a lean combustion exhaust gas. It is an object of the present invention to provide a catalyst coating structure for use and an exhaust gas purification method for purifying NOx in lean combustion exhaust gas with high efficiency and high reliability using the same.

[0011]

Means for Solving the Problems The present inventors have developed an exhaust gas purifying catalyst layer and an exhaust gas purifying catalyst coating structure having high denitration performance in a lean burn region where SOx and steam coexist, and using these. As a result of intensive studies on the exhaust gas purification method, the catalyst A containing silica and calcium and, if necessary, at least one of sulfate, alumina and zirconia in the flow direction of the exhaust gas is provided at the front stage. The present inventors have found that the above-mentioned problems can be solved by arranging the catalyst B containing silver on an alumina carrier having a specific pore structure so as to be arranged at a later stage, thereby completing the present invention.

That is, in order to solve the above-mentioned problems, a first embodiment of the present invention comprises silica and calcium, and if necessary, at least one selected from the group consisting of sulfate, alumina and zirconia. The relationship between the catalyst A and the pore radius and pore volume measured by the nitrogen gas adsorption method is as follows: X is the total pore volume occupied by pores having a pore radius of 300 Å or less, and the pore radius is 25
The total value of the pore volume occupied by pores of not less than 100 Å and not less than 100 Å is defined as Y, and the pore radius is 10
When the total value of the pore volume occupied by the pores of 0 Å to 300 Å is Z, Y has a pore structure in which 70% or more of X and Z is 20% or less of X. An exhaust gas purifying catalyst layer comprising an alumina carrier and a catalyst B containing silver. The catalyst layer is preferably disposed in a flow space of the exhaust gas in a powdered or molded state.

In a second embodiment of the present invention, there is provided a support substrate having an integral structure made of a refractory material having a large number of through holes, and the above-mentioned catalyst is divided at least on the inner surface of the through hole in the support substrate. The present invention is characterized by an exhaust gas purifying catalyst coated structure formed by coating.

Still further, a third embodiment of the present invention removes NOx in exhaust gas containing hydrocarbons as a reducing agent, which comprises contacting the exhaust gas of an internal combustion engine operated at a lean air-fuel ratio with a catalyst-containing layer. Wherein the catalyst contained in the catalyst-containing layer is the exhaust gas-purifying catalyst layer in the first embodiment or the exhaust gas-purifying catalyst coating structure in the second embodiment. An exhaust gas purifying method is characterized in that the catalyst A is disposed at a front stage and the catalyst B is disposed at a rear stage in a flow direction.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The details of the present invention and its operation will be more specifically described below. (Structure of Catalyst and Production Method Thereof) The catalyst A, which is one of the main components of the catalyst B in the exhaust gas purifying catalyst layer of the present invention,
Alumina, which is one of the optional components, can be prepared, for example, by subjecting aluminum hydroxide powder or gel classified as boehmite, pseudoboehmite, vialite, or norstrandite in mineralogy to 300 to 800 ° C. in air or vacuum. Alumina which is phase-transformed into alumina which is crystallographically classified into γ-type, η-type, δ-type, χ-type or a mixed type thereof by heating and dehydration at preferably 400 to 900 ° C. is denitration. Preferred for performance. Alumina with another crystal structure,
For example, α-type alumina is unsuitable as the catalyst component of the present invention because it has an extremely small specific surface area and poor solid acidity.

The alumina of the catalyst B has a total pore volume X of pores having a pore radius of 300 angstroms or less measured by a nitrogen gas adsorption method as X, and 100 angstroms when the pore radius is 25 angstroms or more. When the total value of the pore volume occupied by pores smaller than less than Y is Y, and the total value of the pore volume occupied by pores having a pore radius of 100 Å or more and 300 Å or less is Z, Y is 70% of Χ. As described above, it is necessary to use alumina having a pore structure in which Z is 20% or less of X. When alumina having a pore structure not satisfying the above-mentioned conditions is used as a carrier in the catalyst B of the present invention, the exhaust gas purifying catalyst constituted thereby has poor denitration performance of exhaust gas in the presence of SOx and water vapor. Was enough.
Therefore, it can be said that alumina having the above-mentioned crystal structure and pore characteristics is suitable as the alumina effective as a main component of the catalyst B of the present invention.

The exhaust gas purifying catalyst layer of the present invention is the following catalyst. The catalyst layer according to the present invention comprises: a catalyst A containing silica and calcium, and further, if necessary, at least one selected from the group consisting of sulfate, alumina, and zirconia; And a catalyst B containing silver in alumina having characteristics. The state of calcium contained in the silica of the catalyst A, and at least one state selected from the group consisting of sulfate groups, alumina, and zirconia further contained therein are not particularly limited. On the other hand, the state of silver contained in alumina in the catalyst B is not particularly limited, and examples thereof include a metal state, an oxide state, and a mixed state thereof. In particular, since the composition of the combustion exhaust gas of an internal combustion engine such as a lean burn gasoline automobile changes depending on the operating conditions, the catalyst is exposed to a reducing atmosphere and an oxidizing atmosphere. Therefore, it is assumed that the state of the active metal constituting the catalyst changes depending on the atmosphere. The starting material of calcium in the catalyst A is not particularly limited, but calcium hydroxide is preferable in terms of durability. When a sulfate group is contained in the catalyst A, it is preferable to use sulfuric acid, calcium sulfate, or the like as a starting material of the sulfate group. The starting material of silver in the catalyst B is not particularly limited.

In the catalyst A according to the present invention, the method of allowing the silica to contain calcium and further at least one selected from the group consisting of sulfate, alumina and zirconia, and the method of allowing the alumina to contain silver in the catalyst B are particularly limited. Instead, conventional methods, such as adsorption method,
A pore filling method, an incipient wetness method, an evaporation to dryness method, an impregnation method such as a spray method, a kneading method, a physical mixing method, and a commonly used known method such as a combination method thereof may be arbitrarily adopted. it can.

The content of calcium in the catalyst A is not particularly limited, but is preferably 10 to 80% by weight in terms of CaO. The calcium content is 1 in terms of CaO
When the amount is less than 0% by weight, the initial denitration performance is excellent, but the activity is lowered at an early stage because the SOx absorption performance of the catalyst A is poor.
On the other hand, if the content exceeds 80% by weight, the dispersibility of calcium is reduced, so that the SOx absorption performance is reduced, leading to an early decrease in the denitration activity, which is not preferable. Next, the weight of at least one selected from the group consisting of sulfate, alumina, and zirconia contained in the catalyst A is not particularly limited, but in particular, alumina and zirconia are 30% by weight in terms of SOx absorption performance.
It is preferably less than. On the other hand, the silver content in terms of metal with respect to the catalyst B is not particularly limited, but is 0.1 to 1%.
It is preferably 0% by weight. If the amount of silver carried is less than 0.1% by weight, the effect is not exhibited, and if it exceeds 10% by weight, the combustion reaction of the hydrocarbon as a reducing agent proceeds preferentially, and the NOx removal characteristics deteriorate.

The catalyst A is dried at a drying temperature of about 80 to 120 ° C. The firing temperature is 200 to 800 ° C, preferably about 400 to 600 ° C. Firing temperature 800
C. is not preferable because the specific surface area of silica decreases and the dispersibility of calcium also decreases. On the other hand, catalyst B
The drying temperature is not particularly limited and is usually 80 to
Dry at about 120 ° C. The firing temperature is 300 to 1
000 ° C, preferably about 400 to 900 ° C. If the firing temperature exceeds 1000 ° C., phase transformation to α-type alumina occurs, which is not preferable. The atmosphere at this time is not particularly limited, but each atmosphere such as in air, in an inert gas, or in oxygen may be appropriately selected according to the catalyst composition.
In addition, each atmosphere may be alternately changed at regular intervals.

In the first embodiment of the present invention, when a catalyst layer for purifying exhaust gas is formed, the catalyst layer is formed into a predetermined shape or a predetermined shape through which a target exhaust gas flows in a powder state. Fill in the space. When the catalyst layer is formed into a molded body, its shape is not particularly limited, and various shapes such as a spherical shape, a cylindrical shape, a honeycomb shape, a spiral shape, a granular shape, a pellet shape, and a ring shape can be adopted. These shapes, sizes, and the like may be arbitrarily selected according to use conditions.

Next, an exhaust gas purifying catalyst-coated structure according to a second embodiment of the present invention will be described. Here, the catalyst-coated structure has a structure in which at least the inner surface of the through-hole is coated with the above-mentioned catalyst in a unitary support substrate made of a refractory material having a large number of through-holes. It is.

The support substrate is provided with a large number of through holes along the flow direction of the exhaust gas. In a section perpendicular to the flow direction, the porosity is usually 60 to 90%, preferably 70 to 90%. And the number is one square inch (5.0
30 to 700, preferably 200 to 6, 6 cm ² )
00. The catalyst is coated separately on at least the inner surface of the through-hole, but may be coated on the end face or side face of the supporting substrate.

As the material of the refractory support substrate, ceramics such as α-type alumina, mullite, cordierite, and silicon carbide, and metals such as austenitic and ferritic stainless steels are used. The shape may be a conventional one such as a honeycomb or a foam, but a preferred one is a cordierite or stainless steel honeycomb supporting substrate.

The method of coating the support substrate with a catalyst includes:
A so-called ordinary wash coat method or sol-gel method in which the catalyst of the present invention sized to a certain particle size is coated separately with or without a binder on at least the inner surface of the through-hole of the support substrate without using a binder. Applicable.
Also, the support substrate is coated with alumina in advance,
This may be subjected to a treatment for supporting the catalytically active substance of the present invention to form a catalyst coating layer. The coating amount of the catalyst layer on the supporting substrate is not limited, but is 50 to 250 g per unit volume of the supporting substrate.
/ L, preferably about 100 to 200 g / l.

Next, an exhaust gas purifying method according to a third embodiment of the present invention will be described. The third embodiment of the present invention uses the catalyst layer of the first embodiment and the catalyst-coated structure of the second embodiment described above, and the CO in the exhaust gas,
Reducing components such as HC and H ₂ are converted to ΝOx and O ₂
Such by contacting the exhaust gas containing excess oxygen from the stoichiometry near required to complete oxidation in an oxidizing component, at the same time ΝOx is reduced decomposed to the N ₂ Η _{2 O,} such as HC The reducing agent also oxidizes CO ₂ and H ₂ O.

In the present invention, the catalyst A is disposed at the front stage and the catalyst B is disposed at the rear stage.
This is for improving the durability performance. The ratio between the catalyst A and the catalyst B may be arbitrarily selected according to the SOx durability performance and the NOx removal performance.

When the HC / NOx ratio of the exhaust gas itself is low, such as the exhaust gas of a diesel engine, the fuel ΗC having a concentration of several hundreds to several thousands ppm in terms of methane concentration in the exhaust gas.
If the system for contacting with the catalyst-containing layer of the present invention is added after the addition of, a sufficiently high NOx removal rate can be achieved. Note that HC referred to here includes paraffinic hydrocarbons, olefinic hydrocarbons and aromatic hydrocarbons, oxygen-containing organic compounds such as alcohols, aldehydes, ketones, and ethers, gasoline, kerosene, light oil, heavy oil A, and the like. Means something.

The gas space velocity (SV) at the time of purifying the combustion exhaust gas of the internal combustion engine operated in the lean air-fuel ratio region using the catalyst-containing layer according to the present invention is not particularly limited. 200,000 over 000h ^-1
h- ¹ or less is preferable.

The denitration rate when the gas composition is constant depends on the type of catalyst and the type of HC. In the case of using the catalyst layer of the present invention, for example, C ₂ -C ₆ paraffin,
For aromatic HC olefins and _C 6 -C ₉ 4
50-600 ° C., 350-550 ° C. for C ₆ -C ₉ paraffins and olefins, 250-500 ° C. for C ₁₀ -C ₂₅ paraffins and olefins.
In order to exhibit a high denitrification rate, it is necessary to set the catalyst layer inlet temperature at 100 ° C. or higher to 700 ° C. or lower, preferably at 200 ° C. or higher to 600 ° C. or lower.

[0031]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples. However, the present invention is not limited to the following examples. (1) Selection of Alumina In order to select an alumina carrier to be used for the catalyst B, a to c fall within the scope of the present invention in various γ-type aluminas having specific surface areas and pore distributions as shown in Table 1. Alumina that enters, and d to g are aluminas outside the scope of the present invention. In addition, the pore distribution of alumina of a to g was measured by a soapmatic manufactured by Carlo Elba.

[0032]

[Table 1] ア ル ミ ナ Alumina specific surface area pore distribution (m ² / g) Y / Χ (%) Z / Χ (%) ─────────────────────────────────a 241 83.2 2.4 b 219 87.0 3.9 c 174 88.4 4.4 d 199 47.0 0.7 e 177 68.5 4.9 f 241 51.0 45.9 g 266 71.1 22. 7 ─────────────────────────────────

(2) Preparation of Catalyst Layer Hereinafter, preparation examples of preparation of each catalyst for constituting the catalyst layer of the present invention are shown as reference examples. (A) Production of Catalyst B: [Reference Example 1] 100 g of alumina hydrate, which is a precursor of γ-type alumina a in Table 1, was immersed in a 300 ml aqueous solution containing 5.36 g of silver nitrate for 10 hours. , 8
Evaporated to dryness at 0 ° C. This was air-dried at 110 ° C., and then calcined in air at 550 ° C. for 3 hours to obtain Catalyst 1. The content of Ag in the catalyst 1 in terms of metal was 4.5% by weight based on the entire catalyst.

Reference Example 2 to Reference Example 12 Similarly to Reference Example 1, except that alumina hydrate which is a precursor substance from which γ-type aluminas b to g shown in Table 1 were obtained was used. Catalyst 2 (Reference Example 2), Catalyst 3 (Reference Example 3),
Catalyst 4 (Reference Example 4), Catalyst 5 (Reference Example 5), Catalyst 6 (Reference Example 6), and Catalyst 7 (Reference Example 7) were obtained. Reference Example 1
Catalyst 8 (Reference Example 8) was prepared in the same manner as in Reference Example 1 except that the silver content was 0% by weight, 2% by weight, 3% by weight, 8% by weight, and 12% by weight. ),
Catalyst 9 (Reference Example 9), Catalyst 10 (Reference Example 10), Catalyst 1
1 (Reference Example 11) and Catalyst 12 (Reference Example 12) were obtained.

(B) Production of catalyst A: [Reference Examples 13 to 19] 20 g of commercially available silica and 40 g of calcium hydroxide were stirred and mixed in 200 ml of pure water, evaporated to dryness at 80 ° C., and further dried. It was dried at 110 ° C. and calcined at 550 ° C. to prepare Catalyst 13 (Reference Example 13). At this time, the weight ratio of SiO ₂ to Ca (OH) ₂ was 1: 2. In addition, catalysts having a mixing ratio of SiO ₂ and Ca (OH) ₂ of 15: 1, 3: 1, 1: 5 and 1:10 were prepared in the same manner, and catalysts 14 to 17 (Reference Examples 14 to 17), respectively. And Further, a catalyst composed of only commercially available calcium oxide was designated as catalyst 18 (Reference Example 18), and a catalyst composed of only commercially available silica was designated as Catalyst 19 (Reference Example 19).

Reference Example 20 and Reference Example 36 In Reference Example 13, calcium sulfate (hemihydrate gypsum) was further added to make the weight ratio of silica, calcium hydroxide and calcium sulfate 2: 4: 3 and 8: 1: 1, 4: 1, 1: 1,
Except that they were prepared to be 4: 3 and 1: 8: 5.
Catalysts 20 to 24 (Reference Examples 20 to 24) were prepared in the same manner as in Reference Example 13, and commercially available alumina was added to the mixture so that the weight ratio of silica, calcium hydroxide, and alumina was 2: 4: 1,
Catalysts 25 to 28 (Reference Examples 25 to 28) were prepared in the same manner as in Reference Example 13 except that the catalysts were prepared so as to be 8: 16: 1, 4: 8: 1 and 1: 2: 1. The catalyst consisting only of the catalyst is referred to as a catalyst 29 (Reference Example 29), and zirconia is added thereto so that the weight ratio of silica, calcium hydroxide, and zirconia is 2: 4: 3, 8: 16: 1, 4: 8: 1.
And catalysts 30 to 33 (see Reference Example 30) in the same manner as in Reference Example 13 except that the catalysts were prepared so as to be 1: 2: 1.
To 33), and a commercially available catalyst consisting of zirconia alone was designated as catalyst 34 (Reference Example 34). In Reference Example 13, commercially available alumina and zirconia were further added to adjust the weight ratio of silica, calcium hydroxide, alumina, and zirconia to 8: 16: 3: 1, 8: 16: 1: 3. Catalyst 3 was prepared in the same manner as in Reference Example 13 except that
5, 36 (Reference Examples 35, 36).

(C) Production of honeycomb catalyst: [Reference Examples 37 and 38] 60 g of the above catalyst 13 was
5 g of alumina sol (Αl ₂ O ₃ solid content 20% by weight) and 120 ml of water were charged into a ball mill pot and wet-pulverized to obtain a slurry. Into this slurry, a 1 inch diameter, 2.5 inch length bored from a commercially available 400 cpsi (cell / inch ² ) cordierite honeycomb substrate
After immersing the inch-shaped cylindrical core and pulling it up, excess slurry was removed by air blow and dried. Then 500
Baked at 30 ° C. for 30 minutes, and coated with 150 g of solid content in terms of dry weight per liter of honeycomb to obtain Ca (OH) ₂ —Si
A honeycomb catalyst 37 having an O ₂ composition (Reference Example 37) was obtained.

In addition, 60 g of the above-mentioned powder catalyst 1 was mixed with 8 g of alumina sol (Αl ₂ O ₃ solid content 10% by weight).
And 120 ml of water were charged into a ball mill pot and wet-pulverized to obtain a slurry. A cylindrical core having a diameter of 1 inch and a length of 2.5 inches penetrated from a commercially available 400 cpsi (cell / inch ² ) cordierite honeycomb substrate is immersed in the slurry, and the excess slurry is air blown. And dried.
Then, it is baked at 500 ° C. for 30 minutes, and coated with 150 g of solid content in terms of dry weight per liter of honeycomb, 4.4.
% Αg / Αl ₂ O ₃ composition honeycomb catalyst 38 (Reference Example 3)
8) was obtained.

The catalysts 1 to 3 of the above-mentioned Reference Examples 1 to 38
The results of evaluating the denitration performance of the exhaust gas purifying catalyst layer formed using No. 38 under various conditions will be described. Example 1 Catalyst 13 of Reference Example 13 and Catalyst 1 of Reference Example 1
Is press-molded, and then pulverized to a particle size of 350 to 5
The particle size is adjusted to 00 μm, and the catalyst 13
Was filled in a stainless steel reaction tube having an inner diameter of 15 mm so that the catalyst 1 was placed in the former stage to form a catalyst layer, and this was attached to a normal pressure fixed bed flow reactor. The weight ratio of catalyst 13 to catalyst 1 was 1: 1.

[Performance Evaluation Example 1] The temperature of the exhaust gas in the reaction tube was maintained at 425 ° C.
O: 750 ppm, kerosene (C ₁ ): 4500 ppm, O
_{2: 10%, H 2 O} : 10%, SO 2: 50ppm, the balance space, a mixed gas consisting of _{N 2} velocity 40,000h
^-1 . In the analysis of the gas composition at the outlet of the reaction tube, the concentrations of NO and NO ₂ were measured with a chemiluminescent NOx meter, and the N ₂ O concentration was measured with a gas chromatograph / thermal conductivity detector equipped with a Ρorapack Q column. . The denitration rate was defined by the following equation. Further, N ₂ O and NO ₂ were hardly generated in any of the catalyst layers of the present invention.

[0041]

(Equation 1)

Examples 2 to 21 and Comparative Examples 1 to 14
The same as the above, except that the catalysts 2, 3, 9 to 11 of Reference Examples 2, 3, and 9 to 11 and the catalysts 4 to 8 and 12 of Reference Examples 4 to 8 and 12 were used instead of the catalyst 1 of Example 1, respectively. Was formed, and an evaluation test using a model gas was performed in the same manner. The catalyst layers using the catalysts 2, 3, and 9 to 11 were Examples 2 to 6, respectively, and the catalyst layers using the catalysts 4 to 8, 12 were Comparative Examples 1 to 6, respectively. Reference Example 15,
16, 20, 22, 23, 25 to 28, 30 to 33, 3,
5, 36 catalysts 15, 16, 20, 22, 23, 25 to 25
28, 30 to 33, 35, 36 and Reference Examples 14, 17
-19, 21, 24, 29, 34 catalysts 14, 17-1
9, 21, 24, 29, and 34 were used in place of the catalyst 13 of Example 1 to form a catalyst layer similar to the above, and an evaluation test was performed using a model gas in the same manner. Catalysts 15, 16,
20, 22, 23, 25 to 28, 30 to 33, 35, 3
The catalyst layers using catalyst No. 6 were used as Examples 7 to 21, and the catalyst layers using catalysts 14, 17 to 19, 21, 24, 29, and 34 were used as Comparative Examples 7 to 14, respectively. Table 2 shows the initial denitration performance and the denitration performance 8 hours after the start of the reaction for the catalyst layers of Examples 1 to 21 and Comparative Examples 1 to 14 described above.

[Performance Evaluation Example 2 (Example 22)] In Performance Evaluation Example 1, the honeycomb catalyst 37 of Reference Example 37 and the honeycomb catalyst 38 of Reference Example 38 were each processed into a cylindrical shape having a diameter of 15 mm and a length of 32 mm. Then, a stainless steel reaction tube having an inner diameter of 15 mm was filled so that the honeycomb catalyst 37 was at the front stage and the honeycomb catalyst 38 was at the rear stage with respect to the flow direction of the exhaust gas (Example 22). The space velocity of the gas to be fed to the catalyst layer of the honeycomb catalyst 38 is 13,000 h ^-1.
An evaluation test was performed using the same model gas as in Performance Evaluation Example 1 except that the evaluation was made. Table 2 shows the initial denitration performance and the denitration performance 8 hours after the start of the reaction together with the results of Performance Evaluation Example 1.

[0044]

[Table 2]

From Table 2, Examples 1 to 22 and Comparative Examples 7 to
No. 14 has an initial denitration performance of 75% or more, and Comparative Examples 1 to
6 showed superior performance. Examples 1 to 22
Maintained a high denitration performance of 55% or more even after reacting for 8 hours under the condition of 50 ppm SOx in comparison with Comparative Examples 7-14.

[0046]

As described above, according to the exhaust gas purifying catalyst layer and the exhaust gas purifying catalyst coating structure of the present invention and the exhaust gas purifying method using the same, SOx and water vapor are contained in the lean combustion exhaust gas. It is useful for purifying nitrogen oxides in combustion exhaust gas of an internal combustion engine because it can reduce and purify nitrogen oxides with a high denitration rate.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI B01J 35/10 301 B01J 35/10 301F // B01J 21/04 ZAB 21/04 ZABA 32/00 32/00 B01D 53/36 102H 102A (31 ) Priority claim number Japanese Patent Application No. 8-355574 (32) Priority date Hei 8 (1996) December 24 (33) Priority claim country Japan (JP) (72) Inventor Atsushi Katakei Atsushi Ichikawa, Chiba Minutes 3-18-5 Sumitomo Metal Mining Co., Ltd. Central Research Laboratory (72) Inventor Kunihide Chino 678 Ichihonmatsu, Numazu City, Shizuoka Prefecture

Claims (6)

[Claims] Claims 1. A catalyst A containing silica and calcium, and the relationship between a pore radius and a pore volume measured by a nitrogen gas adsorption method is such that pores occupied by pores having a pore radius of 300 angstroms or less. The total value of the volume is defined as X, the total value of the pore volume occupied by pores having a pore radius of 25 Å or more and less than 100 Å is defined as Y, and the pores occupied by pores having a pore radius of 100 Å or more and 300 Å or less When the total value of the volume is Z,
A catalyst B comprising silver in an alumina carrier having a pore structure in which Y is 70% or more of X and Z is 20% or less of X, for exhaust gas purification. Catalyst layer. 2. The exhaust gas purifying catalyst layer according to claim 1, wherein said catalyst A further contains at least one selected from the group consisting of sulfate groups, alumina and zirconia. 3. The catalyst according to claim 1 or 2, wherein at least the inner surface of the through-hole in a support substrate having an integral structure made of a refractory material having a large number of through-holes is coated in a divided manner. Exhaust gas purification catalyst coated structure. 4. A method for purifying exhaust gas using a hydrocarbon as a reducing agent, comprising contacting combustion exhaust gas of an internal combustion engine operated at a lean air-fuel ratio with the catalyst-containing layer, wherein the catalyst contained in the catalyst-containing layer is 3. An exhaust gas purifying method comprising the exhaust gas purifying catalyst layer according to 1 or 2. 5. A method for purifying exhaust gas using a hydrocarbon as a reducing agent, comprising contacting combustion exhaust gas of an internal combustion engine operated at a lean air-fuel ratio with the catalyst-containing layer, wherein the catalyst contained in the catalyst-containing layer is An exhaust gas purifying method comprising the exhaust gas purifying catalyst-coated structure according to claim 3. 6. The exhaust gas purifying catalyst layer according to claim 4, wherein the catalyst A contained in the exhaust gas purifying catalyst layer is disposed in a front stage and the catalyst B is disposed in a rear stage in the exhaust gas flow direction. Exhaust gas purification method.